The present invention relates generally to ultrasonic transducers, and, more particularly, to a micro-machined ultrasonic transducer (MUT) substrate for limiting the lateral propagation of acoustic energy.
Ultrasonic transducers have been available for quite some time and are particularly useful for non-invasive medical diagnostic imaging. Ultrasonic transducers are typically formed of either piezoelectric elements or of micro-machined ultrasonic transducer (MUT) elements. The piezoelectric elements typically are made of a piezoelectric ceramic such as lead-zirconate-titanate (abbreviated as PZT), with a plurality of elements being arranged to form a transducer. A MUT is formed using known semiconductor manufacturing techniques resulting in a capacitive ultrasonic transducer cell that comprises, in essence, a flexible membrane supported around its edges over a silicon substrate. The membrane is supported by the substrate and forms a cavity. By applying contact material, in the form of electrodes, to the membrane, or a portion of the membrane, and to the base of the cavity in the silicon substrate, and then by applying appropriate voltage signals to the electrodes, the MUT may be electrically energized to produce an appropriate ultrasonic wave. Similarly, when electrically biased, the membrane of the MUT may be used to receive ultrasonic signals by capturing reflected ultrasonic energy and transforming that energy into movement of the electrically biased membrane, which then generates a receive signal.
The MUT cells are typically fabricated on a suitable substrate material, such as silicon (Si). A plurality of MUT cells are electrically connected forming a MUT element. Typically, many hundreds or thousands of MUT elements comprise an ultrasonic transducer array. The transducer elements in the array may be combined with control circuitry forming a transducer assembly, which is then further assembled into a housing possibly including additional control electronics, in the form of electronic circuit boards, the combination of which forms an ultrasonic probe. This ultrasonic probe, which may include various acoustic matching layers, backing layers, and de-matching layers, may then be used to send and receive ultrasonic signals through body tissue.
Unfortunately, the substrate material on which the MUT elements are formed has a propensity to couple acoustic energy from one MUT element to another. This occurs because the substrate material is typically monolithic in structure and acoustic energy from one MUT element is easily coupled through the substrate to adjoining MUT elements. Therefore it would be desirable to have a way to fabricate a MUT substrate that reduces or eliminates the lateral propagation of acoustic energy.
The invention is a MUT substrate that reduces or substantially eliminates the lateral propagation of acoustic energy. The MUT substrate includes holes, commonly referred to as vias, formed in the substrate and proximate to a micro-machined ultrasonic transducer (MUT) element. The vias in the MUT substrate reduce or eliminate the propagation of acoustic energy traveling laterally in the MUT substrate. The vias can be doped to provide an electrical connection between the MUT element and circuitry present on the surface of an integrated circuit substrate over which the MUT substrate is attached.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.